1. Field of the Invention
The present invention relates to a magnetic head used in a recording and reproducing magnetic element, and more particularly to a thin film magnetic head and a thin film magnetic head slider, and a method of producing the same.
2. Description of the Prior Art
In recent years, magnetic recording/reproducing technology has improved remarkably, and accordingly magnetic recording densities are increasing rapidly year after year. To achieve high density and small size, magnetic disk drive, which is typically a recording and reproducing magnetic element, generally writes data onto a magnetic recording medium by magnetic induction and reads data stored on the medium by a magneto-resistive effect. Two recent trends are for magnetic recording/reproducing systems to use giant magneto-resistive effect type devices to improve magnetic reproduction efficiency, and for recording magnetic elements to use magnetic materials that produce higher magnetic flux densities to offset the decrease in recording magnetic field intensity due to increasingly dense and narrow tracks. In general, however, many of the types of materials used to achieve high density and small size in such devices are highly susceptible to corrosion.
The structure of a typical thin film magnetic head will now be described. The thin film magnetic head has a multilayer cross-sectional structure comprising thin magnetic films and insulating films laminated on a substrate. The magnetic thin films are usually formed by sputtering. The laminated thin films form part of an air bearing surface facing the magnetic recording medium. The air bearing surface section is completed through a lapping step for achieving a higher accuracy in the device height and a washing step for removing residues after lapping. A practical thin-film magnetic head manufacturing process uses an aqueous suspension of diamond abrasive grains and a surfactant agent for lapping, a washing fluid that is a mixture of pure water and a surfactant agent for washing, and pure water for rinsing the washing fluid out. After that, the air bearing surface that will face the magnetic recording medium is coated with an over coat consisting of carbon or other suitable material for higher sliding quality and corrosion resistance. In the subsequent processes, including the completion of the thin film magnetic head sliders and in a thin-film magnetic head assembly process involving bonding of spring suspensions and wiring, the air bearing surface also undergoes washing with a washing fluid that is a mixture of pure water and a surfactant agent and rinsing thereof with pure water, and is then installed in the magnetic disk drive.
During these conventional lapping and washing processes, the metal section including the magnetic thin films on the air bearing surface is exposed to the aqueous solutions. Even after the over coat of air bearing surface is formed, the metal section including the magnetic thin films may be exposed to the aqueous solutions through local defects in the over coat. Protective strength against corrosion has depended on the corrosion resistance of the metal. Since all metals do not have sufficient anticorrosion properties, corrosion may unavoidably occur, depending on the type of a metal selected for use. Such corrosion causes bumps and depressions on the air bearing surface, resulting in degraded magnetic characteristics.
One approach to this problem from the manufacturing side employs a nonpolar hydrocarbon solvent in the lapping and washing fluids instead of using an aqueous solution, but the washing power in particular of such hydrocarbon solvent solutions is known to be considerably lower than that of an aqueous solution. Therefore, water washing is much more effective in achieving a high level of cleanliness of the air bearing surfaces.
A method of suppressing corrosion of the metal thin films that occurs due to the use of such aqueous solutions has been disclosed by JP-A-102710/1989. The method brings another thin film, consisting of a substance having an ionization tendency greater than that of the magnetic thin film, into contact with the recording magnetic thin film section of the magnetic head, and exposes part of this other thin film to the air bearing surface. As a result, the magnetic thin film and the other thin film form a local battery, which causes corrosion to develop from the other thin film, thereby retarding corrosion of the magnetic thin film.
The thin film of the substance having an ionization tendency greater than that of the magnetic thin film, however, must be so formed on the air bearing surface as not to affect the magnetic recording/reproducing qualities; more specifically, it should be formed in such a way that its area is the same as or smaller than that of the exposed area of the recording magnetic thin film on the air bearing surface. It is difficult to provide a thin film consisting of a substance having an ionization tendency greater than that of the magnetic thin film with this small an area on the air bearing surface where the magnetic thin film requiring protection against corrosion is exposed. Therefore, this method cannot provide a sufficient corrosion retarding effect.
In addition, a thin film consisting of a substance having a comparatively great ionization tendency is susceptible to corrosion, so if it is exposed on the air bearing surface, the ensuing corrosion products may become projecting faults, which adversely affects anti-sliding properties with respect to the magnetic recording medium, resulting in poor reliability.
An object of the present invention is to provide a thin film magnetic head and a thin film magnetic head slider and methods of producing the same that can effectively retard corrosion of the magnetic thin film immersed in aqueous solutions during the lapping and washing stages of the manufacturing process.
The problem addressed by the present invention can be effectively solved by providing a recording magnetic element and an external conductor electrically coupled to the recording magnetic element by a lead wire, the conductor having an equilibrium electrode potential in an aqueous solution higher than that of the recording magnetic element alone, and having a surface area larger than the cross-sectional area of the recording magnetic element on an air bearing surface facing a magnetic recording medium. The conductor is exposed on an outer surface of the thin film magnetic head that will be immersed in the aqueous solution.
Use of this method can provide the conductor area necessary for suppressing metal dissolution from the recording magnetic element on the air bearing surface in the aqueous solution. This is because corrosion of the magnetic thin film can be retarded.
As described above, the conductor should consist of a material with an equilibrium electrode potential in an aqueous solution higher than the equilibrium electrode potential of the magnetic thin film alone. More specifically, the conductor is preferably an elemental metal conductor, an alloy conductor, or a chemical compound conductor including a material selected from a group of metals such as Au, Ag, Pt, Ru, Rh, Pd, Os, and Ir, or a group of conductive ceramics such as Al2O3.TiC, SiC, TiC, WC, and B4C.
Corrosion retarding mechanisms will now be described. One mechanism in which a conductor consisting of a material such as those described above retards corrosion of a magnetic thin film placing the magnetic thin film in electrically conductive contact with a conductor having an equilibrium electrode potential higher than that of the magnetic thin film, thereby shifting, that is, raising, the equilibrium electrode potential in an aqueous solution (more specifically, a lapping or washing fluid) into passive region, thereby retarding corrosion of the magnetic thin film. It is known that, generally, a stable passive film is formed on the surface of a metal in the passive region and the metal is immune to corrosion at this potential. Accordingly, it is possible to retard corrosion of magnetic thin films, even if they are susceptive to corrosion in aqueous solutions, by shifting the equilibrium electrode potentials into the passive regions.
In another corrosion retarding mechanism, a natural ultra-thin oxide film is formed on the surface of the magnetic thin film through exposure to air before the magnetic thin film is immersed into a washing fluid, or after it is lapped. This natural oxide film is produced in different states depending on the material of the magnetic thin film. A natural oxide film formed on the surface of a magnetic thin film containing Fe or Co as its major constituent is highly susceptible to destruction. In this state, generally, the Fe or Co dissolves rapidly in the washing fluid and the natural oxide film is destroyed in a very short period of time, resulting in corrosion. The present invention brings a conductor into electrically conductive contact with the magnetic thin film to make its equilibrium electrode potential in the aqueous solution closer to that of the magnetic thin film, or raise its equilibrium electrode potential, as described above, whereby the speed at which the metal contained in the magnetic thin film dissolves can be made too slow to yield sufficient energy for destruction of the natural oxide film formed on the surface of the magnetic thin film, washing of the magnetic thin film can be performed by maintaining a state in which the natural oxide film is prevented from destruction, and corrosion of the magnetic thin film can be retarded.
The corrosion retarding mechanisms described above achieve high corrosion retarding effects if the equilibrium electrode potential of the magnetic thin film in the aqueous solution is as close as possible to that of the conductor. For this purpose, it is effective to make the surface area of the conductor as large as possible, so that the combined equilibrium electrode potential in the aqueous solution of the conductor and the magnetic thin film, which are in electrically conductive contact with each other, is governed by the surface area of the conductor, and therefore approaches the equilibrium electrode potential of the conductor alone.
A thin film magnetic head slider according to the present invention has a substrate having an air bearing surface facing a magnetic recording medium, a magneto-resistive effect type reproducing magnetic element comprising a magnetic thin film formed on the substrate, a metal film for electrically connecting the reproducing magnetic element to the outside, a recording magnetic element that generates a magnetic field, a recording coil for carrying electric current, a metal film for electrically connecting the recording coil to the outside, and a conductor formed outside but brought into electrically conductive contact with the recording magnetic element via a lead wire; and the conductor has an equilibrium electrode potential in an aqueous solution higher than that of the recording magnetic element alone and a surface area larger than the cross-sectional area of the recording magnetic element on the air bearing surface facing the magnetic recording medium.
A method of producing a thin film magnetic head slider according to the present invention comprises a step of forming a recording and reproducing magnetic element, including a magneto-resistive effect type reproducing magnetic element formed by a magnetic thin film, a recording magnetic element that generates a magnetic field, and a recording coil for carrying electric current thereto on an insulating film formed on a substrate; a step of coating the recording and reproducing magnetic element with an insulating over coat; a step of forming a metal film for connecting the reproducing magnetic element and the recording coil to the outside via lead wires so that the metal film is exposed on the external surface of the insulating over coat; a step of forming a conductor exposed on the outer surface of the insulating over coat and brought into electrically conductive contact with the recording magnetic element via a lead wire; and a step of lapping and washing the air bearing surface facing the magnetic recording medium after the step of formation of the conductor; the conductor having an equilibrium electrode potential in the aqueous solution higher than that of the recording magnetic element and having a larger surface area than the cross-sectional area of the recording magnetic element on the air bearing surface facing the magnetic recording medium.
Furthermore, magnetic disk drive according to the present invention includes a thin film magnetic head comprising a recording magnetic element constructed with a magnetic thin film and an external conductor that is in electrically conductive contact with the recording magnetic element, the conductor having an equilibrium electrode potential in an aqueous solution higher than that of the recording magnetic element alone, and having a larger surface area than the cross-sectional area of the recording magnetic element on the air bearing surface facing the magnetic recording medium, thereby achieving outstanding recording and reproducing qualities.